Mancha de Alternaria em erva-doce: etiologia e controle químico

Abstract

Fennel, Foeniculum vulgare Mill, is frequently attacked by fungi that cause leaf spots in the Northeast region of Brazil. Among these organisms, Alternaria genus stand out causing the reduction of the photosynthetic area of these plants. In Brazil there is no record of which species are associated with the Alternaria leaf spot on fennel. Little is known about the Alternaria species that cause the disease, even less is known about the methods of controlling. It should be taken into account that chemical control methods must be applied in a controlled manner, since most of the fennel cultivation in Brazil is used as a food condiment. This study aimed to identify the incidence, as well as aspects related to the epidemiology of leaf spot of fennel plants from crops in the states of Paraíba and Pernambuco. It was intended to establish parameters for the use of effective chemical molecules in the control of the disease. For this purpose, symptomatic fennel plants were collected for the isolation of Alternaria spp. The isolated fungal cultures were preserved and deposited in the collection of phytopathogenic fungi at UFRPE. For species identification, at the molecular level, and comparison of phylogenetic relationships, the following were performed: DNA extractions from the isolates; polymerase chain reactions (PCR) for amplification of gene regions (OPA 10-2, Alt a1, GAPDH, Endo PG); and sequencing the amplified regions. A phylogenetic tree was obtained from maximum likelihood analysis, allowing to identify four Alternaria species associated with fennel, causing disease, among these A. alternata and A. jacinthicola. Subsequently, from an in vitro test, it was possible to identify which chemical molecules can be successful in reducing the mycelial growth of the fungus and consequent mitigation of their effects. One of the A. Alternata isolates, with proven pathogenicity, was tested for the reaction to the fungicides: difenoconazole, flutriafol, procymidone and thiophanate-methyl, allowing to identify which difenoconazole has good prospects of success in the control of Alternaria in fennel plantations in Brazil.